Carrier frequency arrangement



CARRI ER FEQUENGY AHRANGEMENT Filed April 18. 1924 4 Sheets-Sheet l INVENTOR Anoia/Vey Dc-lf.Y 20J 1925. i

11,557,544 H. A. AFFEL l CARRIER FREQUENCY ARRANGEMENT v Filed April 18, 3.924 l4 Sbeetsheet 2 @fwd Mmm/EY 557,544' H. A. AFFEL.

CARRIER FREQUENCY ARRANGEMENT Filed April 18. i924 4 SheetsSqhee't 5 0m Em, w25. 1,557,544

H. A. AFFEL.

CARRIER FREQUENCY ARRANSHLMENT' Filed April i8. 1924 4 Sheets-Showl 4 @Zeg/'Wally l I INVENTOR' web y,

MIUR/Vey Patented Het.. im. M925..

hihihi@ tilt s ein "n with..

caserne irnneunn'cr snimrentnsnr.

To al? io/mm it may concern.:

Be it known that L Herman A. Arret.,

.residing at Brooklyn, in the county Iof yKings and State of New York, have invented certain improvements in Carrier Frequency Arrangements, of which the ,fol-v lowing;l is a specification.

This invention relates to multiplex signaling' and more articularly to frequency arrangements of tie signaling channels in such a systern. o

Multiplex carrier signaling arrangements, as at present developed for commercial opn eration, are of 4four general types:

`(l) Multiplex carrier telegraph systeme in which a group of carrier frequencies all lying Within one range are used for transmitting in one direction While a group of car-A rier frequencies lyingevithin another range are, used for transn'iittingy in the opposite direction. Because of limitations in the design of the apparatus of this type of system it is not expedient to operate with carrier frequencies above about l0 ltilocycles.

(2) Multiplex carrier telephone systems in which the carrier and one side hand' are suppressed at the transmittingstation and the carrier is supplied at the receivingr station by the homodyne method, the saine' carrier frequency being employed in conne@ tion With each two-Way channel for trans mission both Ways. n systems of this type discrimination hetween oppositely directed trausnlissionslis obtained hy balancing' the circuits at the terminals and at repeater points. The carrier frequencies employed in this type of system haveheen related to each other as harmonics of a fundamental frequency of 5,000 cycles, so that the spacing' between successive carrier frequencies is 5,000 cycles. This system will he herein-y after referred to as a type A system. 1

(3) Multiplex carrier telephone systems in Which the carrier is .transmitted along with one side band., the other side hand heine* suppressed. ln this'type ot system different frequencies are used for trfms1ni'.-`

sion cach way for each two-Way channel and all of thefrequencies transmitted in one direction are grouped in one frequency range 'and all of the carrier frequencies transmitting' in the opposite direction are grouped in another frequency range. No balance is used in this system for discrimi netien between oppositely directed frequencies, frequency selectivity being; relied upon for this purpose. The carrier frequencies are not 'derived as harmonics of a common fundamental frequency but are spaced frorn each other about 3,000 cycles, the carrier for each channel being separately generated. Systems of this character will. hereinafter he referred to as type B systems.v

(4) Multiplex carrier telephone systems in which the carrier frequencyvand one 'side band are suppressed at the transmitting station and the carrier supplied at the receiving statioirhy the lioniodynemethod, different carriers beingused for 'transmission in each direction in connection with each tyvdway channel. As in the type B system no balance is employed, frequency selec tivity being relied upon to discriminate between oppositely directed transmissions, the carrier frequencies transmitting in one direction are all grouped in one frequency range and those transmitting in the opposite direction in another frequency range. In this system the carrier frequencies are re- .'ljated to each, other as harmonics of a fundamental frequencyof .about 3,3331/3 cycles andv successive carrier frequencies are separated from each. other hy the .same nulnher of cycles. Systems of this. character will hereinafter he referred to as type C systems.

lt has heen found in practice that systems employing. balance at the term' als and at repeater points in order to discriminate .heu tween oppositely directed transmission are not entirely satisfactory because of the diliticulty ofhalancing over a Wide range of fr'equencies and, consequently," systems in` which the carrier 'frequencies are grouped for transmission in the two different directi'onsare preferred. llt is also desirable in order to minimize cross-talk between sys- .tenis9 that Wherefthe frequencies ere' grou-,pcd the groups should he'the same on all lines of the same pole leed and the sauleV frequency Vrange should loeA employed dit all the lines of the sance polelead for channels transmitting in the saine direction. vAlso the selective arrangements Which are eniployed at terminal and repeater points should he adapted for use in connection 1 with either telephone or telegraph systems. It has also heen found that the superposition of telephone and telegraph channels on `the same telephone line will frequently he desired and in order to prevent intermodule tion between telephone and telegraph sig-' nals, separate repeaters should be provided at repeater points for telephone purposes and for telegraph purposes.

It is proposed by the present invention to so divide up the frequency range employed for carrier transmission and to so locate and direct carrier frequencies that the factors above mentioned will be satisfactorily taken care of, consideration being also ygiven to the different spacings employed between the carriers of the type A, typeB and type C telephone systems so that selectivity may be provided to best meet the conditions involved in all ofthese systems.

These results and obiects 'are accomplished in accordancewith the present invention by:

1) Dividing the economicai carrier range (which may be assumed to extend from about 3 to 30 kilocycles) into two parts with the dividing pointat approxi# mately l() kilocycles. the lower of these ranges `to be considered as 'the telegraph rance and the upper as the telephone range: (2) Further dividiner each of these ransres into two directional `groups of channels-one group transmitting' east in each range yand one group transmitting! west in each range:

(3) Operating the upper ,fzroup of channels of the telegraph range and the lower ,frroup of" channels of the telephone range in the same direction in order to simplify selectivitv at repeater points;

(4) Providing for selective discrimination at repeater points between the three main ranges (two transmittingr one wav and one the other) by which the east groups are separated from the west groups. The particular selettive` arrangements employed comprise preferably a transmission band type of filter (that is, al filter which transmits a band freely but suppresses frecuencies on either side thereof) in .one path of the repeater. and a suppression baud filter (that is` a filter which suppresses a-bad of. frequencies and freelv transmits all fre sisting of a suppression band filter `and a transmission band filter, segregates "the channels transmitting in different directions into their proper groups. These filters may be made up as a part of a repeater unit, and a repeater unit as thus made up may be used 'for aunpliyinrr either teiephone channels or telegraph channels or both. If a given repeater is to be employed for amplifying the telegraph channels only, a lowpass filter will be arrangedat the repeater point to select to the repeater only the telegraph channels, which in turn will be separated by the combination of Suppression band and transmission band filters in accordance with the direction of transmission. l'f the repeater. on the other hand. is to arnplify the telephone' channels only. a high nass filter will be used in connection with it to confine the operation of the repeater to the telephone range. the suppression band filter and transmission kband filterv separatina"- the channelsas to direction'. -Where the reneateris yto ampliv both telephone and telegraphchannels. high and low pass filters will not be used.A y

The .invention inav now be further understood from the following detailed description whenread in connection with the accompanying drawings. Fiaurev l of which is al curvediagram showin!! the transmission characteristics of the filter combinations employed in connection with the invention: Fiets. 2 and S'are charts showing the disposition of the channels of different tvpes oi' multiplex'sristems in accordance with the invention; Figs. 4- to 8 inclusive are schematic diagrams showing the selective arrangements at different types of repeater stations; while Figs. 9 and 10 are schematic diagrams showing how' different types of repeater stat-ions may be employed in the same transmission circuits at different rcpeater points.

Referringr to Fig. l, the curves show the transmission characteristics of filter combinations which may be employed in connection with the present invention. Ashas been previously stated` it is proposed to divide the total carrier range into two parts. one to'be used for telegraph purposes and the other for telephone purposes, the. indiividual channels in the two parts being ouencies on either side of the suppressed band) in the other path of the repeater;

grouped in separate ranges in accordance with tbe direction of transmission, and finaily the upper group of the telegraph range and the lower group of theftelephone range beingarranged to transmit in. the same direction. This divides the available carrier range into three main bands, two of ,which transmit'in one direc-tion and the in- Itermediate one off` which transmits in the f other direction. yIn orderto separate the total carrier range intofthese three main bands, it

is proposed to use two filters, one of which will lie-hereinafter referred to as an A type ofiiiter, and the other of which will be referred to as a B type of filter. The A type offilter is' a Suppression `filter., that is, a fili ter whichsuppresses a. band of-given width iso Les

while ,freely transmitting a range of fre quencies from zero up to the 'lower limit ot thezsuppression band and also a range from the upper liniit oif the suppressed band to infinity. By means of this filter all of the channels translnittingin one direction may frbe selected while the channels transmitted. in the opposite direction will be suppressed. The second type of filter, which will be hereinafter referred to as a l type of' filter, is of the kind known as a transmission baud filter, that is, a lilter which freely transmits a definite band of frequencies while. suppressing all frequencies from zero up to the lower limit of the band andl all tre quencies from the upper limit ot the band to infinity. The B type of filter may therefore be used to select the upper group of telegraph channels antl the'lower group of telephone channels while suppressing the `other channels, it being recalled that thel upper group ot' telegraph channels and lower group of telephone channels are arranged to transmit in the same direction. As shown in the diagram, the A and B types of filters may be arranged to divide the available carrier range into three main subbands at frequencies corresponding to about- '6 kilccycles and 2O lrilocycles.

ln order to select or discriminate between y the telephone part of the carrier range and the telegraph part of the carrier range, a 10W pass filter, hereinafter re'f'erred to as a C type filter, and a high pass filter herein after referred to as a D type of filter, may be employed.v These two filters may hagas their cut-oli1 points so arranged as to divie the tota-l .carrier range into two parts at a frequency corresponding to about l0 kilo' cycles, as illustrated in the drawing.

If the C type of filter is used in combination with` the A and E filters, the C filter confines the range oi' tree transmission to the telegraph part'of thwe range, while the A and B filters divide this part of' the frea quency range'into two parts in accordance with the direction ot' transmission. On the other hand, if the D type filter is used in combination with `the A and B'type filters, free transmission is restricted to the tele phone part of the carrier range, and the A and B filters divide this part of the range into tWo sub-ranges in accordance with the.

direction ot transmission. lf all tour filters are employed, the total carrier range is dividedinto -four parts, two ot which transe mit in one' direction andthe other two ot which transmit in the` opposite direction.

With this understandingof how .the cai-- rier range is to be divided up in accordance with the invention, the4 manner in which the channelsrnaybe allocated in accordance with different types of carrier systems will be clear from Fig. 2. In this figure the free transmission bands of the filters and their 7. hda-13:

cut-off points are represented by the full line curves at the top of the lig-ure, The frequency in kilocycles from zero to 34 is plotted as odinates. Carrier frequencies for telephone channels, where transmitted, are shown in long full line arrows. Where the carrier frequencies are suppressed, they are represented by dotted arrows. The carriers for thetelcgraph channels are repre sented by short arrows. Theside bands of the telephone channels are represented by rectangles. The arrangements f or several different combinations are shown in Fig. 2, the type of the system and the number of the channelsbeing designated in the vertical column at the left of the figure. The arrangement of the frequencies for each system are shown in the horizontal columns of the chart.

The lower horizontal column shows an arrangement involving eight two-way telegraph channels and twotwo-way type C telephone carrier channels. The general scheme ofr dividing the frequency range already described provides a maximum of about ten tWo-way telegraph channels. The ten channels .transmitting in each direction may, for example, have the frequencies represented in thetollowing table:

Freq.

Channel I Channel Transmits to Transrnlts to south `or West north or enst V"Since the type --C telepljione system involves the generation and transmisison ot a` fundamental carrier frequency which is not used for signaling but is transmitted in order that the actual carrier frequencies used for signaling may beobtained as harmonics of the fundamenta-l, it is necessary to omit the two lowest frequencies used for telegraph purposes, as the lower frequency, 31A; ltilocycles corresponds with the fundamental carrier frequency :from which the harmonics are obtained, and the next oney above 3,570 cycles is so near to the frequency assigned :for the fundamental that some of the telegraph nimilulations might heytransmitted in the channel assigned to the fundamental. Since telegraph channels 9 and l0 of the lower group are therefore eliminated because otthe necessity; of utilizingl the range corresponding to lthese channels lat the. bottom of the available carrier spectrum, vthe corresponding frequencies ot channels 9 and l0 at the top ot the telegraph range will also be eliminated, these frequencies being k91/2 and l0 kilocycles.

. Two two-way telephone channels are provided involving carrier frequencies of 131/3,

band of each channel is also depressed. ln'

the case of the channels transmittingn west, the upper side bands are transmitted. and in the case of the channels transmitting east the lower side bands are transmitted.

This arrangement wastes a certain amount of space between the upper telegraph channel and the lower telephone channel. rlhere is also room for a one-way telephone channel at the upper part of the telephone, range. Inasmuch as the carrier is not transmitted, itswould he possible to squeeze in an additional two-way channel (if the cut-oil of the filters is made fairly sharp) by transmittingr thelower side band instead of the upper with telephone channels l and 2. The channel transmittimcr west for the third twoway channel miszht then have a carrier of 20 kilocycles assigned to it, the corresponding' transmitted lower side band occupying' Substantially the range now shown for the upper side band of channel No. 2. The corresponding east channel of the third twoway channel would have the carrier frequency of 30kilocycles assigned to it.' and the lower side band would be transmitted. To permitof the provision of the additional two-way telephone channel would. of course, involve very accurate design of the filtering arrangements.

If desired, the telegraph channels may all be omitted, and a/third two-way channel may be provided by using' the upper part of the telegraph range for the channel transmitting west on a carrier frequency of 6% lrilocycles, the upper side band being transmitted. and the corresponding eastbound channel having assigned hereto the carrier frequency of 30 kilocyeles. In this case a fourth two-way channel may he provided where the filters are carefully designed by transmittingr the lower side hands in connection with the west channels l and'2 and providing two additional carrier frequencies at 20 kilocycles and S31/f, lrilocycles in connection with which the lower side bands are transmitted.

The third horizontal column shows an arrangement involving seven two-way telegraph channels and one modified type A. two-way telephone channel. The type A system involves the transmissicn of a frequency of 5,000 cycles as the fundamental from which the telephone carriers are ob-- tained as harmonics. This involves` the elimination of the frequencies cprrespondingA tq the eastbound telegraph channels 2,

carrier frequencies.

ricami-sae 3 and. e. Consequently ,the corresponding frequencies of the upper telegraph range are also omitted.

ln connection with the telephone part of the range, since it is divided up by the filtering arrangement .into two ranges only capable of transmission in a single direction it is necessary toimodify'the type A system so that the corresponding channels of a given two-way transmission employ different Accordingly, one twoway telephone channel is provided by utilizlng a carrier frequency of l5 kilocycles transymitting' west and a carrier frequency of 25 kilocycles transmitting east. As the carrier frequencies in the type 'A system are all harmonics of 5 kilocycles, and the Side hands are closely spaced to the carrier, the type A system is obviously not very economical where the available range is divided up as herein shown, for no channel involving carrier frequency of 20 kilocycles can be obtained. A second two-way telephone channel may be obtained, however, as indicated in the fourth horizontal column where no telegraph channels are provided. In this case the eastbound channel of the second pair will utilize the carrier frequency of l0 lrilocycles and the corresponding channel in the opposite direction will utilize the carrier frequency of 30 kilocycles. A

ln the fifth horizontal column is shown a combination involving vten two-way tele- `ograph channels and three two-way type B telephone channels. channels transmitting west will have assigned to them the carrier frequencies of 1l, 14 and l kilocycles while the eastbound channels will have carrier frequencies of 23 26 and 29 kilocycles respectively. In this system the carrier is transmitted in con.- nection with each channel, and, as shown, the upper side hands are transmitted in connection with the westbound channels and the lower sidebands in connection with the eastbound channels. Itwill he observed that the available frequency range is practically all utilized by this arrangement.

lf desired, an additional pair of telephone channels constituting an additional two-way telephone circuit may be provided as indicated in the sixth horizontaly column by utilizing' the space assigned to the teleg'raph channels. In this case acarrier frequency of 3.000 cycles will be used for the additional eastbound channel and a carrier frequency of 9,000 cycles will be used for the additional westbound channel. l

Fig. l illustrates in lschematic form an arrangement of repeaters which may be employed at a repeater station where both telephone and telegraph channels are provided. lt will benoted that the carrier channels are selected 'from the ordinary telephone transmission by means of a high pass filter desig- The three telephone Maaate nated HP in the drawing, so that 'all-ot the carrier channels may he amplified Without disturbing in any Way the ordinary telephone part. of the system. Flor carrier yainpliication it will be noted that. two repeater units are provided, one for .amplifying the telephone channels and the other for ainplitying the telegraph channels. Each ot these sets consists oit two paths, each path including a one-way amplilier,'and an A type filter in the one path and a B type iilter in the other path on either side ci the *ampli lier. The tWo sets are identical and conse-- quently the repeater units may he nia-de vup with the il and li .filters tor use either for telephone purposes or telegraph purposes. 'C type lilters are interposed on either side of the. telegraph repeater unit and l) type lilters on either side of the telephone repeater units. The C type filters select the telegraph part ot' the range from the telephonel part and transmit the corresponding channelsto the telegraph repeater. The A and B typelilters in the repeatt then function to divide the east hound channels from the Westbound channels at the point of separation, which,

in the cases illustra-ted, corresponds to 6 lillo. cycles. vConsequently the eastbound chan--' nels are amplified hy the am litier ot the one path While the westbound c annels are am# plitied by thea-mplifier ot the other path. o balancing arrangements are necessary Vat the repeater point.

lnasmuch as the telephone part of the range involveshigher frequencies than the telegraph part, it may he necessary to provide additional repeater stations at which only the telephone channels will he amplilied, and no repeater Will he provided at such. stations for amplifying the telegraph frequencies. ,Such an arrangement is illustrated in Fig. 5 in which the telephone repeater unit is identical with that illustrated in Fig. Ll and the lilter arrangement is the saine. Vrlhe telegraph channels, however, are

ley-passed around the repeater through theY C type filters Wit-h no repeating unit in eluded in the bypass. llie schematic lay out shown in Fig. 9 will indicate a typical circuit arrangement involving the two types oi' repeaters. As shown at the terminal sta tions, the carrier frequencies are all taken oli' through the usual high pass tilter HP, and `C and l) type filters are provided to separate the carrier telegraph channels 'from the carrier telephone channels so that the two types ol circuitsmay he treated at the terminal separately. The lirst repeater station nearest the terminal would, in general, he a repeater station ot the type shown in Fig. 5, as the telegraph. channels Ta'ould'not he Yattenuated as much as the telephone channels at this point. At the next station rcpcai'er apparatus oi' thc type shown in Fin'. l might he employed ,for amplifying both thc telephone and the telegraph channels. The third station again might he of the type shown yin Fig." 5 in which only the telephone channels are amplified.

Where the enti-rc range is used tor telephone purposes, or, on the other hand, Where no telephone channels at all are provided hut only telegraph range is used for telegraph purposes, a repeater oi' the type shown in Fig. (l may he employed. Here no C and l) lilters are necessary, but all of the channels in the three main ranges are passed to the repeater 'through the high pass'filters lill, and in the repeater the ranges are separated by' the i and i3 lilters in accordance with the direction of transmission. As has already heen observed, the type A system is not Well'adapted to the general scheme ot dividing up thefrequency range as already described, and where type A systems are to he provided aslight modiication should he made as illustrated hy the chart in Fig. 3. This modification involves segregating the telegraph range-from thel telephone range by means ot (l and D filters and only providing A and B filters in connection with the telegraph part ot' the range, so that the telephone part of the range may Ahe employed for transmission in either d1- rection. rllhis is indicated in Fig. `3 hy the dotted line portions oli the characteristics of the A. and Btiltere Which are supposed to represent portions of `the frequency spectrum in which the A. and -B filters are inetlectivebecause their action is conlined to a range previously selected by the C type filter. i

Referring to the lower horizontal column of Fig. 3, an arrangement is shown involving seven carrie-r telegraph channels and three type i telephone channels. The telephone channels are all eontlned to the telephone `part of the carrier range and have assigned to them.y carrier frequencies ot' lo,

20 and :25 liilocycles. @Wing to the tact that' the frequency ci 5,000 cycles is used for the fundamental trom 'which the telephone carriers are generated, the three nearest tele` graph channels are omitted so that only seven channels remain. lt will readily he Seen that at any point where it is necessary to separate the telephone and telegraph vparts of thc total carrier, range the telegraphtrequencies may he selected into an appropriate circuit by a C filter and the telephone frequencies into another appropriate circuit by a D tilter. It" in the former circuit'l and B filters are employed, the action ot the A and B filters will merely be to 4' separate the groups of channels transmit ting in opposite directions Without prod-uov ing any similar separation in the telephone part ont the. range.l Consequently 1t is possible to use the saine carrier for transmission both Ways in the telephone part of the range, and at repeater points appropriate types of repeaters may he employed for telephone purposes as will he described later.

If, instead of using the telegraph part of 6 the rangefor telegraph purposes, it is desired to employ this portion of the spectrum for an additional two-wayytelephone channel, the` C and D filters may `he omitted as Well as the A and B filters in which case the 10 arrangement will be as indicated in the second horizontal column of Fig. This gives fourtyp'e A systems of the ordinaryptype with thechannels arranged exactly as in type A systems of the prior art. If, on the l5 other` hand, it is desired to use the circuit only for telegraph purposes, the C and D filters may be omitted and only the A and B filters used, the latter filters in thiscase separating thc channels transmitting in opposite directions as before. This will give ten complete telegraph channels as Aindicated in 'the third horizontal column of Fig. 3.

A repeater arrangement suitable for use in connection with a system such as is 'laid out in the lower horizontal column of Fig. 3 is illustrated in Fig. 7. lt will he noted lthat the telegraph repeater is identical with the telegraph repeater of Fig. 1i. The C filter functions to select into the telegraph repeater circuit the frequenciesl lying in the telegraph range only, and the A and B filters in the repeater circuit itself then discriminate between oppositely directed channels within the range selected hy the filter C.

The telephone repeater is of the two-way two-repeater type as indicated at RE and RW. Since the same carrier .is `used for transmitting in both directions, oppositelydirected channels cannot be separated hy frequency discrimination, but halance'must be employed. The D filters at the terminals 0f the repeater serve to select and transmit to the repeater frequencies lying Within the telephone carrier range only, and these frequencies may be in either direction.

The balancing arrangement is somewhat complicated but. may be readily understood. On the artificial line side of the circuitbeyond the terminals of the hybrid coil l0, for example, a D filter is provided to balance the D filter on the line side of the circuit. yond the D filter the network is vranched, and one branch includes a C networv to simulate-the .impedance of the C filter inthe telegraph repeater' branch while the other branch of the net includes a. high pass filter y to balance the high pass filter HP of the highfrequency composite set. Beyond the high pass filter HP in the network two Abranches are provided, one including a low pass network having an impedance equivaent to the low pass filter LP of the high fre quency composite set. The other branch des- @5 ignated in the drawing as the B network 'sitely directed groups of the subrange sesimulates the impedance of the line section itself.

As already discussed in connection with Figs. 4 and 5, some repeater installations need make no provision for amplifying the frequencies in the carrier telegraph range. Atsuch stations the circuit arrangement may be as indicated in.Fig. 8. This figure differs from Fig. 7 in that thetelegraph repeater is omitted and the telegraph channels are transmitted directly through aby-pass including C type filters. The telephone part of the repeater installation is identical with that in Fig. 7.

F'g. l0 shows schematically a typical sys tem employing repeaters of the type shown in Fig. 7 and also of the type shown in Fig. 8. As the principles of the layout of Fig. l0 are similar to those of Fig. i), no further description thereof is deemed necessary.

fn the foregoing description referencehas been made to certain definite frequencies for' the'purpose of giving concrete examples. It will beunderstood, however, that the principles of the invention are independentA of the particular frequencies and frequency ranges hereinbefore referred to. It will also be` understood that the-general principlesv herein disclosed may he embodied in many other organizations widely different from those illustrated without departing from the spirit of the invention as defined in the following claims.

lVhat is claimed is:

l. A selective arrangement to be em'y ployed in connection with a multiplexcarrier system in which vthe carrier range is dividedginl'o two suhranges, each of which is split into two directional groups of channels transmitting in opposite 'directions of which the adjacent groups of the two subranges are operated in the same direction, comprising 'i low pass filter for selecting the lower suhrange into one path, a high pass filter for selecting the upper subrange into another path, means in said first path comprising a combination of a band suppression filter and a band transmission filter for discriminating between thetwo' 'oppolected, and means in the other path comprising a combination of a band suppression filter and a band transmission filter identical with the filters in the first mentioned path vfor discriminating between the oppositely directed groups of the subrange selected into the path.

2. A selective arrangement to be employed in connection with a multiplex-carrier system in which the carrier range 1s 125 l divided into two subi-anges, each of which is split into two directional groups of'channels transmitting in opposite directions of which the adjacent groups of the two sub ranges are operated in the saine direction, 130

Learnit comprising a low pass filter to select the lower subrange in the one path, a high pass filter to select the higher subrange into another path, means in said first mentioned path to discriminate between oppositely directed groups, said means comprising` a combination of' a band suppression filter and a band transmission filter7 the band suppressed by the suppression filter being coincident with the band transmitted by the band transmission filter, and means in the said second mentioned path for discriminating between oppositely directed groups, said means comprising a combination consisting of Ek-band suppression filter and a band transmission filterl identical with the corresponding filters in said first'mentioned path.

3. ln a multiplex carrier system in which the available carrier range is divided. into two subranges and one, at least, of the subranges is further split into two directional groups of channels each group transmitting in opposite directions, fa selecting arrangement comprising a high pass filter for selecting one subrange into one path, a low pass filter for selecting the other subrange into another path, and means in one 4of said paths for discriminating between the oppositely directed groups of channels. said means comprising a combination of' a band suppression filter and a band transmission filter, the band suppressed by the suppression Filter being coincident with the band transmitted by the transmission filter.

4. ln a carrier system in which the available carrier range is divided into two subranges cach ot' which is split into two directional groups of channels transmitting in opposite directions of :which the. adjacent groups of both subranges are operated in the same direction,A a repeater station comprising separate two-repeater lcombinations for amplifying the two subranges, the twoi repeater arrangements being identicalin construction and each comprisinr two oppositely directed paths, one of w ich includes a band suppression filter and the other of which includes a band transmission filter for discriminating between oppositely directed groups transmitted through the repeater, and a high pass filter in circuit with one repeater and a low pass filter inwcircuit with the other repeater to select one subrange into one repeater and the other subrange into the other.

5. ln a carrier system in which the available carrier range is divided into two subranges each of which is split into two directional groups of channels transmitting in opposite directions of which adjacent groups of both subranges are operated .in the same direction, a repeater station comprisingsep'arate two-repeater combinations for amplifying the two subranges, the tworepeater arrangements being identical in construction and each comprising two oppositely directed paths, one of which includes a hand suppression filter and the other of which includes a band .transmission filter for discriminating between oppositely drected groups transmitted through the repeater, the band suppressed by the suppression filter and the band transmitted by the transmission filter being identical, andra high pass filter in circuit with one repeater and a low pass filter in circuit with the other repeater to select one subrange into one ref peater and the other subrange into the other.

vIn testimony whereof, l have signed my name to this specification this 17th day oii April. 1921i.

y HERMAN A. AFFEL. 

